A couple things:

1.) Was anything recently changed?  Carb worked on, fuel filter changed, fuel pump changed?  If so see what went wrong, because that's your most likely cause.
2.) Fuel pump putting out too much pressure and blowing the needle off the seat, not allowing it to seal and shut off the fuel flow. Carbs want at most about 7psi.
3.) Needle stuck open due to contamination.  Ethanol fuel can be the culprit here.  My generator used to get stuck like this all the time from sitting with E10 fuel in it.  I started adding 1oz. per gallon of Startron to it when I put it away and its never happened since. 
4.) As stated, a problem with the float or float level.  Not knowing what carb it is I can tell you that the "factory" setting for the Autolite carbs was almost always wrong from my experience and would cause this exact problem.  I always had to adjust the level lower until it stopped doing what you carb is doing.  Holleys you should be able to go by sight plugs.  Never had a float issue on an Edelbrock. 

Last edited by TKOPerformance (11/26/2018 7:05 PM)

Almost certainly a gunked up needle and seat I'll bet.  If its ever going to sit for more than a couple weeks with fuel that has ethanol in it I'd add that Startron to it at 1 oz. per gallon.